But if a user delete a file, there is no way to restore just this file.My user are very stupid and they are delete the junk to.

Actually the only way is:

1- Extract the tar.gz save.2- Open with text editor <extracted folder>/databases/files/files_file3- Search the name of wanted file <title> example-file.extension </title>4- Find the id folder of file. 1 line up <folder_id>XX</folder_id>5- Go to <extracted folder>/files/folder_XXXX6- And find the good folder version and copy paste you're file into only office.